IMO it's in the eyes of the buyer. A continuation CSX Cobra has a relatively narrow value range. A period 427 side oiler would typically add value/appeal because it makes the replica closer to an original competition or S/C model. But those motors are generally not more expensive than a current alloy 427 from Shelby. Almost all, if not all, of the street 427 Cobras were fitted with 428's even though the cars were called and badged "427's". Some buyers would prefer a period 428 over a current 427 and others would not. The biggest shortcoming of the ebay csx is that it's fiberglass rather than aluminum, and that's the biggest value determinant for continuation Cobras. The ebay Cobra was a great buy. The next owner will likely pay much more the next time it sells. :cheers